Torsional vibration in the internal combustion engine is a well-known problem. This vibration is the consequence of a variation in the crankshaft speed of rotation, driven by fluctuations in the delivery of torque from the pistons to the crankshaft. The firing frequency of the engine is usually the largest constituent of the crankshaft torsional vibration.
One response to torsional vibration in the internal combustion engine has been the provision of vibration dampers. A common choice of vibration damper is the pendulum damper. This type of damper has been used in aircraft engines and, more recently, has been used in the torque converters of production automotive engines. The pendulum damper is thus well known for suppressing engine vibrations. This suppression is accomplished by tuning the pendulum to resonate at the engine firing frequency. In particular, pendulum dampers have been employed to balance or cancel out undesirable order vibrations of an engine. In these cases, the crankshaft is connected to the pendulum mass by rollers that in different ones of the references move in circular, cycloidal, or other paths in an attempt to keep the pendulums' resonant frequency in accordance with the engine's firing frequency at all engine speeds.
Known pendulum dampers are designed to prevent mechanical damage to the engine by preventing swing amplitudes of the pendulum masses beyond their mechanical limits or capacity. In these known dampers the pendulum masses at low amplitude swing angles almost completely cancel engine vibrations by tracking of the rollers along a path which generates approximately tautochronic motion of the pendulums. At higher or greater amplitudes, these arrangements provide a method of automatically detuning the pendulums whereby they progressively become less and less tuned to the excitation frequency of the crankshaft. This results in a progressive decrease in the response of the pendulum to the vibrational impulses, which limits the swing amplitude at higher torsional vibration excitation levels to maintain the pendulum mass within the mechanical limits of its swing angle capacity.
While pendulum dampers have proven effective at reducing torsional vibration in the internal combustion engine, known pendulum dampers do not provide a perfect solution to the vibration problem. Of particular concern is the fact that the placement of the rollers is generally limited to lubricated environments. However, placement of the rollers in a non-lubricated environment such as on the flywheel of a dry clutch may result in early failure and thus raises durability concerns.
As in so many areas of vehicle technology, there is always room for improvement related to the systems and methods to reduce the amount of torsional vibration produced by the internal combustion engine.